Help: Everything keeps freezing/Slowing Down

A few days ago I opened Google Chrome but it froze before the start up page could load. My computer then froze for a short while before the spinning wheel came up. I managed to quit Chrome but when I re-opened it it happened again. I stopped using Chrome and used Firefox instead but now every 10 minutes or so it freezes too! Many of my games also now freeze up/crash making them impossible to play.

What should I do?

EDIT: Completely forgot to say that after those incidents it has been taking at least 10 minutes to turn the system on. Finder also freezes sometimes when I open it and on the most recent turn on of my computer the dock was reset to factory settings.